1. The Field of the Invention
Implementations of the present invention relate, generally, to the field of reducing environmental pollution during transport or storage of liquids. More particularly, implementations of the present invention are adapted for use in openings for the filling of large transportation and storage tanks, known as manholes.
2. The Relevant Technology
The present invention relates to the liquid storage and transportation industry. In particular, implementations of the present invention relate to the sealing of manholes used as access points to large storage and transportation tanks. These tanks are commonly used in the containment of liquids such as gasoline, diesel fuel, heating oil, and other fuels; acids; alkalis; and other liquid chemical products. Many of these liquids are volatile compounds or may otherwise enter the atmosphere. Even those that are not particularly volatile may have negative environmental impacts if spilled from their containers.
Environmental pollution concerns from tank filling are similar to pollution concerns from filling an automobile gas tank. On a small scale, the problem can be overcome with a vapor control nozzle, as are commonly used in the automobile fueling industry. However, the challenge is amplified on the scale of a bulk transport tank. A typical tanker trailer can hold up to 11,600 U.S. gallons. Due to the large capacity of the trailers, the filling rates must be large, as well. A common filling method is the discharge of liquids into a large opening in the top of the tank called a manhole. The liquid is delivered to the manhole through a conduit known as a loading boom. Loading booms can deliver liquid at a rate of 50-100 gallons per minute or more. Despite being a seemingly smaller effect than spills, vapors released during the filling process may escape and, in sum, account for a larger release of a compound than from spills of liquid. Therefore, a number of solutions have been proposed aimed at reducing the chance or effect of both sources of pollution from the filling of bulk transport tanks.
For instance, one device consists of a filler tube and vapor recovery vent incorporated into a single, cylindrical body that is lowered into place within a manhole. The filler tube allows for the loading boom to discharge liquid into the tank without constraint, and the vapor recovery vent can be connected to a vapor recovery system. Thereby, the filling station can fill the tank at the conventional rate while capturing the vapors generated during the filling process. The body is lowered into place and fixed there with a lockdown bar across the top of the device. The entire device hangs from the lockdown bar affixed the top of the manhole at contact points. The contact points and the lockdown bars allow the device to be secured to the manhole in only two positions that are offset from one another by 180 degrees.
The device has a flexible tube stretched around the perimeter of the device between an outer wall of the body of the device and the interior wall of the manhole. The flexible tube can be deployed to create an annular seal around the cylindrical body. However, while expanding radially, and eventually against the interior wall of the manhole, the tube also expands longitudinally. Inflation of the seal is, therefore, imprecise. Mere contact between the tube and the wall does not ensure a robust seal, while increased inflation undesirably expands the tube longitudinally, leading to overinflation and weakening of the tube.
Likewise, the device includes a recessed top area that can lead to a number of problems. The recessed top area can act as a well that can accumulate dirt, gravel, ice, water, snow, or any other airborne debris that occurs at filling stations or during storage of the device. This can make the device less reliable or slower to use, as well as shorten the life of the connections housed in the body.
Thus, there are a number of problems that can be addressed with manhole sealing devices.